Container flooring material and method of manufacture

ABSTRACT

A board suitable for use as container flooring uses bamboo and fast-growth low-density wood. Thin layers of high-density bamboo composites are used to overlay on surfaces of a core layer which can be the composite of wood veneer and wood strand-based composite, or wood veneer and bamboo stripe sheet composite. This invention combines the benefits of bamboo and wood materials to produce a bamboo-wood composite board having sufficient mechanical and physical strength and durability for use as container flooring.

CROSS REFERENCE TO RELATED APPLICATIONS

Pursuant to 35 U.S.C. § 119(a), this application claims the benefit ofearlier filing date and right of priority to Chinese Application No.031528414, filed on Aug. 27, 2003 entitled “A Kind of Container Flooringand Its Manufacturing Method”, the contents of which are herebyincorporated by reference herein in its entirety.

BACKGROUND OF THE INVENTION

The present invention relates to a composite board suitable for use as acontainer flooring material.

Container shipping revolutionized the shipping industry in the 1950's. Acontainer body could be moved from a tractor-trailer and placed itfully-loaded on a ship, a railroad car, or even an airplane. Oceanshipping in this manner saves the tedious, expensive, and time-consumingjob of unloading cargo from a truck or a railroad car, loading it intothe hull of a ship and reversing the process at the ship's destination.A standard container can carry up to 20 tons (U.S.) fully loaded. It cankeep shipments together, protect them from the elements, from damage inhandling, and from theft. An estimated 90 percent of the world's tradetoday moves in containers.

The floorboard of the container is the main structural component tocarry the cargo loading. Container flooring must meet high requirementsfor mechanical performance, impact resistance, and durability. For manyyears, the container industry has relied on high-density hardwoodspecies from the tropical forest to produce the multiple-layer thickplywood as container floorboards. However, tropical high-densityhardwood species such as Apitong and Keruing face increasing demandwhile having very long growth cycles. As a result, tropical hardwoodforests are rapidly diminishing.

To protect the natural environment and decrease the consumption oftropical hardwood, it would be desirable to develop a new type ofcontainer flooring with a more environmentally-friendly species toexpand the floorboard supply and meet the increasing demand of thecontainer industry.

SUMMARY OF INVENTION

The present invention relates to a novel wood composite materialsuitable for use as container flooring. Rather than using tropicalhardwood species, the present invention utilizes fast growing bamboospecies, as well as fast-growing low-density wood species such as poplaror aspen.

Therefore, in one aspect of the invention, the invention may comprise abamboo-wood composite board comprising: (a) at least one surface layercomprised of a plurality of bamboo stripe sheets and resin; (b) a corelayer comprising at least one wood veneer layer and a support layer.

The support layer may comprise a wood-strand layer or it may compriseanother wood veneer layer. If there are more than one wood veneer layer,preferably the grains of the layers are disposed perpendicularly.

In another aspect, the invention may comprise a bamboo-wood compositeboard comprising: (a) at least one surface layer comprised of aplurality of bamboo stripe sheets and a resin; (b) a core layercomprising a wood strand layer.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows one embodiment of the invention in cross-section. Thefloorboard has a core layer composed of wood veneer and strand-basedwood composite. Item (1) is the surface layer of thin high-densitybamboo composite; Item (2) is the poplar or other wood species veneer inthe parallel direction; and Item (3) is the strand-based wood composite.

FIG. 2 shows another embodiment of the invention in cross-section. Thefloorboard has a core layer composed of wood veneer and bamboo stripesheets. Item (1) is the surface layer of thin high-density bamboocomposite; Item (2) is the wood veneer in the parallel direction; Item(3) is the wood veneer in the perpendicular direction; and Item (4) isthe bamboo stripe sheet in the perpendicular direction.

FIG. 3 shows another embodiment of the invention in cross-section. Thefloorboard has a core layer composed of wood veneer. Item (1) is thesurface layer of thin high-density bamboo composite; Item (2) is thewood veneer in parallel direction; and Item (3) is the wood veneer inperpendicular direction.

DETAILED DESCRIPTION

When describing the present invention, all terms not defined herein havetheir common art-recognized meanings. As used herein, the term “about”refers to a margin of plus or minus 10%, or within the tolerance of asuitable measuring device or instrument. As used herein, “specificdensity” refers to density relative to water. All wood density refers tothe density of oven-dried wood.

The present invention relates to a bamboo-wood composite board suitablefor use as a container flooring material. In general terms, theinvention comprises a multilayer board having a surface composite bamboolayer and a wood core layer. The wood core layer may be comprised ofwood veneer layers or a wood strand layer, or both wood veneer and woodstrand layers.

The bamboo layer comprises bamboo stripe sheets made of strips of bambooand a suitable resin. The bamboo strips may be arranged so that thebamboo strips are all parallel, or parallel and perpendicularcombination, or they may be layered or woven in a crisscrossing pattern.The bamboo strip sheets are pressed into a thin high density bamboolayer which preferably has a specific density of at least about 0.9.

The wood core layer may comprise wood veneers in either grain parallelor grain perpendicular orientation or in alternating parallel andperpendicular layers. As used herein, “grain parallel” refers to woodgrain which is parallel to the longitudinal axis of the board. “Grainperpendicular” refers to wood grain which is perpendicular thelongitudinal axis of the board. As well, or alternatively, the wood corelayer may comprise a wood strand layer, which comprises wood strandchips similar to those suitable for use in oriented strand boards. Thewood strand layer may be oriented or non-oriented.

The wood core layer, either wood veneers or wood strand, or both a woodveneer and a wood strand layer, may preferably be comprised of anysuitable low-density wood. Low density wood has a specific density ofabout 0.6 or less. Suitable wood species may include poplar, aspen,spruce, fir and pine. Preferably, the wood species is a fast growingspecies which may provide a plentiful and low-cost supply.

In one embodiment, the invention comprises a wood composite materialcomprising bamboo and a low-density wood species as raw materials. Asshown in FIG. 1, the material includes at least one surface layer (1) ofthin high-density bamboo composites and a core layer of a wood strandlayer (3). Optionally, a buffer layer of a wood veneer (2) may bedisposed between the bamboo surface layer (1) and the wood strand layer.In one embodiment, the surface layer of thin high-density bamboocomposite (1) is bonded to a wood species veneer (2) such as a poplarveneer in the parallel or perpendicular direction and a strand-basedwood composite layer (3), which may or may not be oriented.

The bamboo composite may be formed by processing bamboo culms intobamboo stripe sheets and hot-pressing the resinated bamboo stripe sheetsinto thin high-density bamboo composites. The wood veneers andstrand-based wood composites may be formed using techniques well-knownto those skilled in the art.

In one example, the bamboo culms are processed into bamboo stripes andwoven into bamboo stripe sheets. About 3 to 7 layers of these bamboostripe sheets may be resinated with a suitable mixture ofphenol-formaldehyde resin and insecticide and then conditioned anddried. These bamboo stripe sheets are then formed them into a mat whichis hot-pressed with the press temperature of about 135 to about 145° C.and press pressure of about 4.0 to about 4.5 MPa for about 6 to about 10minutes. Preferably, the press pressure is gradually reduced fordegassing or the press cooled with cold water. Resin may then be appliedto the surface of the bamboo composite layer for the next step.

Poplar log may be processed into strands, such as those strands suitablefor oriented strand board (OSB) and pressed into the strand-basedcomposite with or without orientation The wood strand layer may then besanded to the target thickness for the core layer (3).

The middle wood veneer layer may be a poplar veneer layer having athickness of between about 1.0 to about 2.0 mm and a moisture contentless than about 8%. Both sides of the veneer are coated with resin (theresin is mixed with the insecticide) at a loading rate of about 300 to400 g/m². The veneers may then be conditioned and dried.

Using the thin high-density bamboo composite as the surface layer (1),the wood strand-based composite as the core layer (3), and a layer ofwood veneer between them (2) to form the mat, the mat is then pressedwith press temperature of about 135 to about 145° C. and press pressureof about 1.5 to about 3.0 MPa for 10 to 18 minutes while graduallyreducing the press pressure for degassing or cooling the press with coldwater.

The mechanical and physical properties of the resulting floorboard are:

MOR in parallel direction: ≧80 MPa

MOR in perpendicular direction: ≧30 Mpa

MOE in parallel direction: ≧10,000 MPa

MOE in perpendicular direction: ≧3,000 Mpa

Panel density: 0.75 to 0.85 g/cm³

In an alternative embodiment, the bamboo composite layers, the woodveneer and the wood strand layers may be pressed without prepressing thebamboo layer. This method may reduce the processing time however; it maybe more difficult to control the density of the bamboo layerconsistently.

In another embodiment as shown schematically in FIG. 2, the floorboardcomprises surface bamboo stripe sheets and a core layer composed of woodveneers and bamboo stripe sheets. The surface layer of thin high-densitybamboo composite (1) is bonded to a wood veneer (2) in the paralleldirection, a wood veneer in the perpendicular direction (3), and abamboo stripe sheet in the perpendicular direction (4).

In one example, the thin high density bamboo composites may be formed asdescribed above. A poplar veneer as described above is coated on bothsides with resin loaded at about 300 to 400 g/m² may then be conditionedand dried.

The floorboard may then be formed using two layers of thin high-densitybamboo composites as surface layers (1), two layers of bamboo stripesheets as the fortified layers (4), and seventeen layers of wood veneersas the core layer, preferably with alternating grain direction, (2) toform the mat with a structure of twenty-one layers. The mat furnish isthen pressed with press temperature of 135 to 145° C. and press pressureof 2.0 to 3.0 MPa for 35 to 40 minutes, gradually reducing the presspressure for degassing or cooling the press with cold water, and openingthe press for the final product.

The mechanical and physical properties of the resulting floorboard are:

MOR in parallel direction: ≧80 MPa

MOR in perpendicular direction: ≧30 Mpa

MOE in parallel direction: ≧10,000 MPa

MOE in perpendicular direction: ≧3,000 Mpa

Panel density: 0.70 to 0.85 g/cm³

In another embodiment shown schematically in FIG. 3, the floorboardcomprises a core layer (2, 3) composed of wood veneers running in bothparallel and perpendicular directions and a surface layer of thinhigh-density bamboo composite (1).

The bamboo stripe sheets and the thin high-density bamboo composite maybe formed as described above. As well, the wood veneers are also formedas described above. Resin is applied to the both sides of the poplar orChinese red pine veneers whose moisture content is less than 8% andthickness is between 1.0 to 2.0 mm (the resin is mixed with theinsecticide), loaded at 300 to 400 g/m², followed by conditioning anddrying.

Using two layers of thin high-density bamboo composites as the surfacelayers (1), and seventeen layers of poplar or Chinese red pine veneersas the core layer to form the mat with a structure of nineteen-layers asshown in FIG. 3, the mat furnish is pressed with press temperature of135 to 145° C. and press pressure of 2.0 to 3.0 MPa for 35 to 40minutes. Again, the press pressure is preferably gradually decreased fordegassing or the press cooled with cold water.

The mechanical and physical properties of the resulting floorboard are:

MOR in parallel direction: ≧80 MPa

MOR in perpendicular direction: ≧30 Mpa

MOE in parallel direction: ≧10,000 MPa

MOE in perpendicular direction: ≧3,000 Mpa

Panel density: 0.70 to 0.85 g/cm³

Without being restricted to a theory based on the mechanical theory ofthe composite material, it is believed that the contribution to theentire MOE of individual layer in the symmetrical multiple-layerstructure is in proportion to its MOE to the third power of its distanceto the central plane. Accordingly, the layer with the high MOE will havea higher contribution to the overall MOE of the structure when it islocated in the outer region (i.e. far away from the center plane). Inthe meantime, the region near the center plane of the composite willinherit the maximum shear force. Therefore, the floorboard manufacturedby this invention will combine the characteristics of bamboo and woodmaterials to meet standard requirements of mechanical and physicalproperties in the container industry.

As will be apparent to those skilled in the art, various modifications,adaptations and variations of the foregoing specific disclosure can bemade without departing from the scope of the invention claimed herein.The various features and elements of the described invention may becombined in a manner different from the combinations described orclaimed herein, without departing from the scope of the invention.

1. A bamboo-wood composite board comprising: (a) at least one surfacelayer comprised of a plurality of bamboo stripe sheets and resin; (b) acore layer comprising at least one wood veneer layer and a supportlayer.
 2. The board of claim 1 wherein the support layer comprises awood strand layer or a wood veneer layer oriented perpendicular to theat least one wood veneer layer.
 3. The board of claim 2 wherein the corelayer comprises least four layers of wood veneers, alternating betweengrain parallel and grain perpendicular layers.
 4. The board of claim 3wherein the support layer further comprises at least one bamboo stripesheet.
 5. The board of claim 3 wherein the core layer comprises 17layers of wood veneers, alternating between grain parallel and grainperpendicular layers.
 6. The board of claim 3 comprising two surfacebamboo layers, sandwiching the core layer.
 7. The board of claim 2wherein the support layer comprises a wood strand layer.
 8. The board ofclaim 7 wherein the wood strand layer is an oriented strand layer. 9.The board of any preceding claim wherein the wood comprises a woodhaving a specific density of about 0.6 or less.
 10. The board of claim 9wherein the wood comprises poplar, aspen, spruce, fir, or pine.
 11. Abamboo-wood composite board comprising: (a) at least one surface layercomprised of a plurality of bamboo stripe sheets and a resin; (b) a corelayer comprising a wood strand layer.
 12. The board of claim 11 whereinthe wood strand layer comprises a low-density wood material.
 13. Theboard of claim 12 wherein the low-density wood material is selected fromthe group consisting of poplar, aspen, spruce, pine or fir.
 14. Theboard of claim 11 further comprising a wood veneer layer disposedbetween surface bamboo layer and the wood strand layer.
 15. The board ofclaim 11 wherein the wood strand layer is an oriented strand layer.